In many electronic systems, it is necessary to determine the phase of the vector sum of a pair of orthogonal signals with respect to one of its components. For example, in digital TV receivers, it is convenient to perform automatic flesh color correction by manipulating the phase and magnitude of the chrominance vector. The chrominance signal, is usually available in the form of two quadrature signals represented by the I and Q color mixture signals or the (R-Y) and (B-Y) color difference signals. Thus, to perform the required manipulation, the phase of the chrominance vector must be determined from its perpendicularly-disposed component parts.
It is well known that the instantaneous phase of the vector sum of a pair of orthogonal signals may be ascertained by generating the arctangent of the ratio of the instantaneous magnitude values of the respective signal components --i.e., .theta.=Arctangent (Q/I). Typically, this is accomplished by using a read-only memory (ROM) to which tan .theta. (i.e., Q/I) values are applied as address codes, and which is programmed to contain the associated .theta. values at the respective memory locations.